Earth can be likened to one big, planetary magnet. Likewise, Earth’s magnetic field is similar to that of a bar magnet tilted 11 degrees from the spin axis of the Earth. The magnetic field serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation.

Like the invisible force shield around the Death Star, Earth’s magnetic field surrounds and protects our planet from the hottest, most statically charged particles the sun can throw our way. This shield – the natural product of molten iron swirling around the planet’s core – has had our backs for billions of years, and prevented Earth from becoming an irradiated, electrified wasteland.

But were you to use a compass at varied points throughout history, you would be in for a huge surprise, like seeing the compass’ needle pointing in the opposite direction than expected. When South becomes North and North becomes South, all sorts of unexpected and dangerous things can happen. A new study suggests that we’re not only overdue for a pole reversal but that such events happen much faster and suddenly than previously thought.

In the new study, an international team of scientists analyzed 16,000 years of geomagnetic history coded into the atoms of an ancient stalagmite in China. This story written in stone told them that once, about 98,000 years ago, the planet’s magnetic field suddenly flipped polarity in as little as 100 years – roughly 30 times faster than the generally expected rate and 10 times faster than what was thought to be the fastest rate possible.

A stalagmite is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. The rock itself is composed partly of magnetite, which can become magnetized by the planet’s magnetic field, allowing geologists to use it as a record of Earth’s magnetic history. This new study findings were published in the journal Proceedings of the National Academy of Sciences.

Study co-author Andrew Roberts, a professor of Earth sciences at Australian National University, said, “The record provides important insights into ancient magnetic field behavior, which has turned out to vary much more rapidly than previously thought” and further added, “Hopefully, such an event is a long way in the future and we can develop future technologies to avoid huge damage.”